This invention relates to construction materials having limited cohesive strength, and particularly composite boards such as hardboard, particle board, and the like and to joinder of such materials in the construction process. Such materials, in the form of boards, panels and the like, may be used to fabricate many structures, such as boxes, doors, door jambs and casings, etc. They are desirable as construction materials because they are generally less expensive than materials such as plywood and lumber. However, they are more difficult to join together by driven fasteners, such as nails and staples, because of their frangibility or susceptibility to cleavage. Frequently, when a nail is driven through such a low cohesion board and into an abutted board or other construction member to join them together, the board will fracture at the exit position by impact of the penetrating nail, cleaving or dislodging fragments from the board which will be pushed by the nail in between the abutting surfaces of the boards to separate them. The result is a loose and insecure joint. This disability has heretofore limited the use of desirably inexpensive composite boards for many construction applications and particularly for prefabricated structures and substructures for buildings and the like.